1. Field
The present embodiments generally relate to signaling systems. More specifically, the present embodiments relate to efficient techniques for calibrating and optimizing signaling systems based on measured channel characteristics.
2. Related Art
As technological advances continue to make digital signaling systems faster, it is becoming increasingly harder to accurately determine voltage and timing margins for these systems. These voltage and timing margins are used both to determine the performance of the signaling system and to calibrate signaling operations by determining an optimal sampling point.
Existing techniques for characterizing voltage and timing margins use very long and complex pseudo-random bit sequences (PRBS) which exercise possible transition sequences and to thereby stress the system. For example, referring to FIGS. 1A and 1B, the timing margins for a high-speed communication channel obtained using less complex PRBSs are significantly larger than the timing margins obtained using PRBS15 (215-1 bits). More specifically, both the eye height and eye width for the channel decrease as the complexity of the PRBS increases. Note that there exist significant differences in voltage and timing margins determined using PRBS7 and corresponding margins determined using PRBS15. Also note that the curves do not plateau at PRBS15. Consequently, PRBS15 does appear to reflect the worst-case voltage and timing margins.
Unfortunately, it is impractical to routinely measure or simulate a digital system using PRBS15 (or a longer PRBS) because the required time to use PRBS increases exponentially as the complexity of the PRBS increases.
Hence, what is needed is a method and an apparatus for determining the performance of a digital signaling system without the above-described problems.